Stage lighting fixtures are known which are provided with a casing, a light source adapted to emit a light beam, a reflector coupled to the light source and at least one beam processing element (such as a dichroic filter, a gobo disc, a dimmer), adapted to selectively intercept the light beam for processing it.
A heat-shield filter is arranged between the light source and the beam processing elements, which divides the casing substantially into a first area comprising the light source and into a second area comprising the light beam processing elements.
A lighting fixture of this type is described for example in documents U.S. Pat. No. 4,890,208 and U.S. Pat. No. 5,515,254.
The area comprising the light source is characterized by high temperatures and is generally cooled by means of a cooling assembly comprising at least one fan arranged in the proximity of an air outlet for aiding the circulation of cold air coming from outside the casing.
The heat-shield filter is substantially configured so as to produce a heat barrier between the area in which the light source is housed and the area in which the beam processing means are housed. In detail, the heat-shield filter is configured so as to filter the hot radiations (radiations which cause an increase in the temperature of the body on which they impinge) in the field of non visible radiations. This prevents the hot radiations in the field of non visible radiations from impinging on the light beam processing means (dichroic filters, gobo assemblies, dimmers), thereby heating them.
However, in the lighting fixtures of this type it often happens that the heat-shield filter becomes excessively overheated. In fact, the hot radiations produced by the light source and the hot radiations in the field of visible radiations reflected by the light beam processing means (for example, by the dichroic filters, by the dimmer) impinge on the heat-shield filter.
The overheating of the heat-shield filter contributes to increasing the temperature of the area comprising the light source and in particular, of the light source bulb portion proximal to the heat-shield filter. Such phenomenon causes an uncontrolled overheating of the light source which, most of the times, causes irreversible damage to the light source.
This implies the unreliability of the lighting fixture and obvious inconveniences for the end user.